1. Field of the Invention
The present invention relates generally to the design and manufacture of printed circuit board (PCB) assemblies. More particularly, it relates to improved techniques of mounting components on a printed circuit board (PCB) assembly.
2. Description of the Prior Art
Modular construction techniques are widely used to manufacture various electronic devices, including computer apparatus and computer peripherals. With modular techniques, a manufacturer can economically assemble several variations of an electronic device using different combinations of pre-assembled modular circuits, which they typically mount on removable printed circuit boards (PCB's). Additionally, modular construction permits vendors to routinely assemble and/or service different variations of an electronic system at a point of sale. Further, end users are often capable of adding, removing or replacing some modular electronic components with little effort and skill. Indeed, some manufacturers have fabricated optional electronic components as small add-in cards that users plug into narrow slots accessible to the exterior of the apparatus. For instance, laptop, palmtop, and other portable computers, as well as a variety of mobile intelligent electronic devices frequently employ small add-in cards and slots, which function as peripherals or other optional circuits.
One particular add-in device is referred to as a PC Card, a trademark of the Personal Computer Memory Card International Association (PCMCIA), which sets standards for their construction. A typical PC Card, also called a PCMCIA card, is approximately the size of a credit card and includes a low-profile PCB assembly sealed within a slender housing. One standard type of PCMCIA card is only about 3.3 millimeters thick and is intended to be used primarily as a memory-related peripheral. A second type of PCMCIA card is approximately 5 millimeters thick and accommodates devices such as modem, fax and network cards. A third type of PCMCIA card, which is about 10.5 millimeters thick, accommodates devices that require more space, such as wireless communications devices and rotating storage media (such as hard disks).
When fabricating PCMCIA cards and other compact PCB structures, manufacturers often employ surface-mount technology (SMT), which relates to techniques of fixing components directly to the surface of a PCB instead of soldering them into holes pre-drilled for that purpose. Advantages of using SMT include device compactness, resistance to vibration, and a capacity for dense interconnections on both sides of a PCB. These advantages make SMT particularly suitable for fabricating conventional PCMCIA cards and other low-profile electronic devices.
Because PCMCIA cards and similar devices normally contain a surface-mounted PCB sealed within an enclosure, their internal components are generally inaccessible to a user. Thus, manufacturers seldom include components within a PCMCIA card or similar device that commonly need servicing. Circuit components that are transient in nature, such as protective fuses and relays, usually mount away from a PCMCIA card. In those instances where the fuse mounts away from the PCMCIA card, e.g., in a separate enclosure mounted within a computer apparatus, a user or service facility can usually replace or reset the fuse with little effort. However, in those instances where a protective fuse mounts within a PCMCIA card, a user would need to return the PCMCIA card to a manufacturer for servicing or replacement whenever a component failed, e.g., when a fuse opened. To service a fuse in a PCMCIA card, a manufacturer would usually need to unseal the enclosure, replace or reset the fuse, and reseal the PCB, usually in a new enclosure. In many situations, manufacturers find it less expensive to simply send the user a new PCMCIA card rather than service to old one.
Those concerned with the development of PCMCIA cards and like devices have recognized the disadvantages associated with the inaccessibility of such devices. While locating switches and fuses away from a PCMCIA card can make those components more accessible to a user, it usually increases the overall construction costs to a manufacturer of a computer apparatus. By using the alternative approach, i.e., surface mounting switches and fuses in a PCMCIA card, the initial manufacturing costs can be lessened. However, that approach will normally increase the overall maintenance and servicing costs of such devices. Notwithstanding the cost factors, it is not always possible to locate certain components within a PCMCIA card. Many of the conventional surface-mountable components that are small enough to fit within the limited space available in a typical PCMCIA card do not have the required voltage ratings. For that reason, manufacturers must mount those components in the computer apparatus away from a PCMCIA card or like device. Consequently, those concerned with the development and manufacture of electronic equipment have long recognized a need for improved techniques of designing PCMCIA cards and other compact PCB structures.